Use screen with custom baud rates on FTDI devices

ftscreen.sh

#!/bin/bash
# since screen doesn't know how to set custom baud rates, this does it for FTDI devices.
# it works by using setserial to set the custom speed (spd_cust) mode for baud rate 38400
# it calculates the proper clock divider by dividing the device's base clock by the desired rate
# then, it starts screen at 38400 - which is not longer 38400 but your new clock rate.
# tested on FT232H, FT2232H, FT-X, and FT232RL
# does not work on CH341 or PL2303

# todo: confirm FTDI before running setserial and report error
# todo: validate uart range

# default baud and port
baud=115200
port=/dev/ttyUSB0

#parse params
for param in "$@"
do
	# if it starts with / its a device
	if [[ $param == /* ]]; then port=$param
	# else if its all digits, its baud rate
	elif [[ $param  =~ ^-?[0-9]+$ ]]; then baud=$param
	# otherwise error
	else echo "$0 [port] [baud]
parameters optional and ok in any order, and default to 115200 and /dev/ttyUSB0"l; exit 1
	fi
done

# get base clock via setserial, and calculate baud
baud_base=`setserial $port -G | sed "s/.*baud_base \([0-9]*\).*/\1/"`
divisor=$(($baud_base/$baud))

# debug output
#echo baud = $baud port = $port baud_base = $baud_base divisor = $divisor

# set baud rate and run screen if successful
setserial $port spd_cust divisor $divisor && screen $port 38400 && exit 0

# if we made it here, setserial probably failed
echo custom baud rates only work on FTDI devices. Double check your device and port.